Police found an 11cm blade buried inside a chocolate mud cake supplied for a meeting attended by Mayor Len Brown, prompting fears of an attempt to harm him.

Yesterday, Detective Senior Sergeant Richard Wilkie confirmed a blade had been found inside a cake supplied for a meeting at Manurewa's Alfriston College.

Organisers discovered the blade when they cut into the middle of the $45 cake, which was about to be served to Brown, senior police officers and local school children.

The incident is revealed in documents issued to the Herald on Sunday under the Official Information Act. After questions from the newspaper, police confirmed they had purchased the cake for a meeting with the mayor.

The cake was supplied by a popular South Auckland cake shop, Windmill Bakery, and picked up by a police officer.

The bakery's manager told an investigator that the blade must have been from a box cutter, which had inadvertently fallen into the box containing the cake.

But the report noted the blade had been found buried in the cream layer in the middle of the cake.

The Food Safety Authority's report into the incident in August last year says: "It would be disappointing if it were established that the blade had been placed purposefully in the cake once the identity of the purchaser was known to the bakery, however this is a possibility we cannot discount at this stage."

Photographs show Len Brown attended the school meeting, held to promote special high-tech marking of school property to deter thieves. A spokeswoman for the mayor said yesterday that he had not been told a blade was discovered in the cake.

This week, bakery manager Van Ngo said the blade was not placed in the cake deliberately.

"When they made the order we didn't know it was police - just the phone number and person's name," he said. "We didn't know where they came from."

It is one of the most dangerous objects found in food in the past 12 months, according to a register of complaints to the Food Safety Authority.

The register reveals 80 food outlets around the country were investigated because of complaints.

Customers reported finding a range of items in their food, from maggots in sausage meat to insects in dumplings, a sticking plaster in a sausage roll and a fly in a pie. One North Shore complainant found the tail and bones of a mouse in a piece of battered chicken.

Others lost teeth or fillings after biting into pieces of metal in various foods.

Ngo said stress had contributed to the blade being buried in the cake. "I think the baker was too hurried - too many orders," he said.

Investigators issued an official warning to the bakery, and its food safety grading was dropped from "A" to "B".

Staff now used pre-cut boxes.

He was "very sorry" about what had happened and said it was the only complaint he had received in 10 years about a foreign object in his food.

MAF spokesman Geoff Allen said many of the cases were due to machine breakdowns and human error, which were difficult to prevent.

Ten of the investigations resulted in official warnings to the manufacturer, and another 11 were referred to other authorities. Nine received an advisory letter.